Unfortunately, there are a couple of other rules that sometimes affect the use of the silent ‘e’. And the word ‘have’ is a good example.
For centuries the ‘u’ and the ‘v’ were considered the same letter. The ‘v’ was usually used, probably because it was easier to carve in stone or write with a quill pen. It was not until about the 16th Century that the ‘u’ became a vowel and the ‘v’ became a consonant.
The modern English spelling rule states that no word may end in ‘v’ or ‘u’. If a word should logically end in either of these letters a silent ‘e’ must be added. Today there is no regular English word that ends in ‘v’ but plenty that end in ‘ve’.
The letter ‘u’ is a different matter. During the 20th Century a host of foreign words that end in ‘u’ invaded the English language. Some examples are ….kudzu, jujitsu, mumu, guru, emu, gnu, impromptu. Today, many of these words are deeply embedded in our dictionaries and the rule no longer seems to apply to the letter ‘u’. But it still applies to the letter ‘v’.
If a word may now end in a solitary ‘u’ (flu) there is no longer any valid excuse for not fully accepting ‘thru’. It is now common in many businesses (Drive Thru) and is used everywhere by highway departments. ‘No Thru Traffic”.
This ungainly word ‘through’ is the only one of the ‘ough-augh’ words that has the ‘oo’ sound. Eliminating it would be the first step towards getting rid of all the words in that archaic group.